The present invention relates to delivery systems for targeting contrast agents for improved diagnosis of tumors by X-ray imaging and to methods for diagnosis, prognosis and follow-up of treatment of tumors comprising administration of the delivery systems to patients followed by X-ray imaging.
Although treatment of breast carcinoma, the most common malignancy among women, is improving steadily by means of surgical intervention and chemotherapy, prognosis depends heavily on early detection. In most developed countries, women aged 40-50 are urged to undergo annual mammography examinations. Ever since it was first introduced, mammography has improved in terms of its spatial resolution and the decrease in the required radiation dose. Yet there are limits on the size of detectable lesions, within permissive radiation doses, that are dictated by the very small density differences between malignant and normal tissues. Even the most advanced mammographic apparatus are limited in their tumor identification capacity. Although anatomical details are clearly portrayed, unequivocal identification is sometimes difficult.
The selective delivery of agents to specific organs is intended in general to specifically localize a delivered agent in the target organ while maintaining low levels in blood and other organs. Ideally, a targeting vehicle, e.g., antibody, which binds selectively to eptopes on specific cells, may be used for targeted delivery of therapeutic or diagnostic agents. Antibody-mediated delivery is, however, often restricted by lack of good antibody specificity (suitable antibodies for breast carcinoma are not available at present but they exist for other organs), limited specific uptake by the target tissue, low penetration and high prolonged levels in blood and other organs (Epenetos et al,1986; Welch, 1987).
Various other strategies have been developed for drug targeting, some of which are based on carrier-mediated delivery which employ natural ligands recognized by receptors or target cells. Most of these systems utilize macromolecular carriers armed with targeting ligands recognized by specific cell types. Certain targeting ligands are known, the most common are terminal saccharide residues recognized by receptors on liver parenchymal (Gal and GalNac of asialoglycoproteins, Ashwell et al, 1982) and non-parenchymal cells (GluNac and Man, Taylor et al, 1992), B-cells (Lasky et al, 1989) or endothelial cells (Bevilacqua et al, 1989). Recent developments in peptide chemistry and molecular biology yielded diverse peptide libraries consisting of numerous random peptide sequences (Pasqualini et al, 1996). Peptides with specific biological activity capable of mediating selective localization in tissues such as lung (Johnson et al, 1993) or lymphocytes (Cepek et al, 1994) have been obtained. An important example is the recently reported families of angiogenesis suppressing/inducing integrins that suppress or encourage the generation of new blood vessels (Varner et al, 1996; Folkman, 1996). These proteins are adhesion receptors not present in normal tissue but appear on endothelial cells of blood vessels of neovasculating areas. Since neovascularization is typical of malignant tissues at a certain stage, substances that interact with integrins might be considered as tissue markers for contrast agent delivery to blood vessels in neovasculating tumors (Brooks et al, 1994; Arap et al, 1998). Systematic screening of chemically-modified proteins (Neurath et al, 1995; Fujita et al, 1994) also yielded products recognized selectively by specific cells, for example, aromatic acid anhydrides that block CD4 cell receptors for HIV-1. Several systems were described that utilize macro-molecular carriers armed with targeting ligands recognized by specific cell types (Monsigny et al, 1994; Hashida et al, 1995).
Tissue-targeting research and practice also utilize several alternative approaches. Some rely on physiochemical properties leading to passive uptake and accumulation, such as inherent accumulation of the agent by the target tissue (e.g., iodine by the thyroid). An important mechanism is the enhanced permeability and retention (EPR) phenomenon whereby molecules of a certain size may diffuse through blood vessels in areas of neovascularization as in malignant tissues (Matsumura et al, 1986; Duncan et al, 1996). Although this mechanism is not specific in terms of organ and type of the malignancy, a contrast agent may be delivered to all neovasculating lesions by means of EPR, thus providing important pathological and anatomical information for many types of tumor.
The intense activity in the field of targeting drugs to specific organs, tissues or cells have yielded a variety of carrier systems such as pro-drugs, liposomes, e.g., sterically stabilized liposomes (SSL) (Kedar et al, 1994) or polymers, both natural and synthetic. The carrier conveys the drug to the specific tissue (via antibody or a tissue marker) where the drug executes the therapy. Attempts to use selective delivery for diagnosis by targeting contrast agents are not as common, though MRI or sonographic agents are under examination. On the other hand, scintigraphy, based on the accumulation of radioisotopes in particular organs or in cancer lesions, is commonly practiced in clinics. X-ray absorbing agents, such as barium and iodine, are being used routinely in non-specific administration.
Citation of any document herein is not intended as an admission that such document is pertinent prior art, or considered material to the patentabilty of any claim of the present application. Any statement as to content or a date of any document is based on the information available to applicants at the time of filing and does not constitute an admission as to the correctness of such a statement.
It is an object of the present invention to provide a delivery system and a method for tumor diagnosis, prognosis and follow-up of cancer therapy by using macromolecular carriers with or without specific tissue markers, for delivering heavy metals with an atomic number (hereinafter indicated by xe2x80x9cZxe2x80x9d) within the range 75-92, to selected organs or sites for tumor-enhanced X-ray imaging.
Another object of the present invention is to use the same delivery system and method for delivering lower Z elements which have the property of an abrupt discontinuity/change in their X-ray attenuation coefficients, and whose attenuation threshold is within the X-ray energy range used for the specific radiography technology selected (e.g., mammography, computed tomography, digital radiography). Thus, the images obtained from two parts of the X-ray energy spectrum, one above the threshold and one below the threshold, can then be used to digitally generate a difference image having superior contrast. The two images can be generated either by filtering the impinging radiation or by analyzing the detected radiation according to the above threshold and the below threshold contributions. All elements with Z in the range of 33-50 progressively exhibit such a discontinuity/change in X-ray attenuation coefficient in the 10-30 keV range within which all mammography is applied.
The present invention thus relates to a delivery system for targeting a contrast agent to specific organs for the purpose of tumor diagnosis, prognosticating the effectiveness of chemotherapy in treating cancer and for follow-up of cancer therapy by X-ray imaging, where the delivery system includes a conjugate or complex of a macromolecular carrier and a contrast agent selected from: (a) a compound of a heavy element with an atomic number in the range of 75-92, and (b) an element with a property of an abrupt change in its X-ray attenuation coefficient within the energy range used for radiography, where the macromolecular carrier may be optionally linked to a specific tissue marker.
The present invention further relates to methods for tumor diagnosis, for prognosticating the effectiveness of chemotherapy in the treatment of cancer, and for follow-up of cancer therapy by X-ray imaging, which involves administering to a patient an effective amount of a delivery system of the present invention, followed by X-ray imaging of the patient. As a non-limiting example, the delivery system is used for diagnosis, prognosis and/or follow-up of chemotherapy for breast cancer.
The following abbreviations are used throughout the specification:
ADH: adiric acid hydrazide; BSA: bovine serum albumin; CDDP: cis-diamminedichloroplatinum II (cisplatin); CMdex: carboxymethyldextran; DDW: double-distilled water; EPR: enhanced permeability and retention; Hydr (H in the figures): hydrazine or hydrazide; OPDA: o-phenylenediamine; Ova: ovalbumin; St: streptavidin; TNP: 2,4,6-trinitrophenyl.